Is the Jeep Grand Cherokee a good/ reliable car?

If the vehicle has been properly maintained then yes it could be reliable. Before purchasing it i would take it to a mechanic and get their opinion after they do a inspection. 

As other people mentioned repairs would be much cheaper due to the amount of used/aftermarket parts available. 

Well, IMO 20+ years old vehicles cannot be considered reliable unless they have been maintained exceptionally well.  

We love my 2002, we loved my '98, and we loved my '95. Not much more to say. People keep saying they break down a lot but none of mine have spent any time in the shop at all. Tune ups, minor issues. One of my pulleys just started screeching one day, cost $100 to fix.

We have had  five (5) of them in our family not yet have we had a transmission to go out. three of them were I6 4.0  AND 2 W/ V- 6 3.7

2002 JGC  4.0  88,200   MILES      2007 JGC  125,000 W/3.7 V-6

2005 JEEP LIBERTY  165,000 MILES V-6 3.7

There is no way to say that a 10-20 year old vehicle is reliable. It depends on how the individual vehicle has been taken care of.

They are not reliable but parts are cheap and there are tons of them in junkyards.

The first generation was solid but better to look for the second gen, the WJ platform from 99-04 was very robust. It is just not fuel efficient. The next generation, the WK was cheapened up by the the Diamler Benz influence, very plastic cheap interior and it lost the venerable 4.0 l6 motor.

http://www.wjjeeps.com/

many people like older Jeeps but they have many problems such as the intake manifold cracking and brake calipers seizing up.

Vehicles of any brand that are 15+ years old cannot be considered reliable unless they have been well-maintained and driven gently by their owners. That rules out the vast majority as being reliable. I have a 28 year old Toyota that is reliable because ?I have owned it since new and taken really good care of it. As a rule, older Japanese cars are far more reliable than Americaqn-made ones.